First Working version of the Emergengy pusher.

.gitignore

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+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch

.vscode/extensions.json

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+{
+    // See http://go.microsoft.com/fwlink/?LinkId=827846
+    // for the documentation about the extensions.json format
+    "recommendations": [
+        "platformio.platformio-ide"
+    ],
+    "unwantedRecommendations": [
+        "ms-vscode.cpptools-extension-pack"
+    ]
+}

.vscode/settings.json

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+{
+    "files.associations": {
+        "array": "cpp",
+        "string": "cpp",
+        "string_view": "cpp"
+    }
+}

include/README

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+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the usual convention is to give header files names that end with `.h'.
+It is most portable to use only letters, digits, dashes, and underscores in
+header file names, and at most one dot.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:esp32doit-devkit-v1]
+platform = espressif32
+board = esp32doit-devkit-v1
+framework = arduino
+monitor_speed = 115200

src/main.cpp

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+#include <Arduino.h>
+#include <esp_now.h>
+#include <WiFi.h>
+ 
+// GPIOs
+#define GPIO_EMERGENCY_LED 5
+#define GPIO_SYNC_LED 19
+#define GPIO_EMERGENCY_BUTTON 16
+
+// Software Parameters
+#define LOOP_DELAY 1
+#define PING_TIMEOUT_NUM_LOOPS 2
+#define EMERGENCY_BUTTON_SCAN_RATE_SECONDS 2
+
+String macList[2] = {"24:6F:28:B1:EE:74", "24:6F:28:B2:40:8C"};
+String macLocal,macRemote;
+uint8_t macRemoteIntArr[6];
+esp_now_peer_info_t peerInfo={};
+int64_t lastPingUptimeInSeconds;
+volatile int64_t lastButtonPushUptimeInSeconds;
+boolean isReceiverEmergencyLedOn;
+volatile boolean isSenderEmergency;
+
+typedef struct struct_info {
+  boolean isEmergency;
+  boolean isPing;
+  String macOfSender;
+} struct_info;
+struct_info myData;
+
+
+int64_t getUptimeInSeconds(){
+  return esp_timer_get_time()/1000000;
+}
+
+// Callback when data is sent
+void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
+  Serial.print("\r\nLast Packet Send Status:\t");
+  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
+}
+
+// Callback when data is received
+void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
+  struct_info myData;
+  memcpy(&myData, incomingData, sizeof(incomingData));
+  Serial.print("Bytes received: ");
+  Serial.println(len);
+  Serial.printf("d:_%d_|",myData.isPing);
+
+  if (myData.isPing) {
+    lastPingUptimeInSeconds=getUptimeInSeconds();
+  } 
+
+  if(myData.isEmergency) {
+    digitalWrite(GPIO_EMERGENCY_LED,HIGH);
+    isReceiverEmergencyLedOn=true;
+  } else {
+    digitalWrite(GPIO_EMERGENCY_LED,LOW);
+    isReceiverEmergencyLedOn=false;
+  }
+}
+
+void OnButtonPushed(){
+  Serial.println("BUTTON PUSH CALLBACK.");
+  if((getUptimeInSeconds()-lastButtonPushUptimeInSeconds)>EMERGENCY_BUTTON_SCAN_RATE_SECONDS){
+    isSenderEmergency=!isSenderEmergency;
+    lastButtonPushUptimeInSeconds=getUptimeInSeconds();
+    Serial.println("BUTTON PUSH EXEC.");
+  }
+}
+
+int char2int(char input)
+{
+  if(input >= '0' && input <= '9')
+    return input - '0';
+  if(input >= 'A' && input <= 'F')
+    return input - 'A' + 10;
+  if(input >= 'a' && input <= 'f')
+    return input - 'a' + 10;
+  throw std::invalid_argument("Invalid input string");
+}
+
+// This function assumes src to be a zero terminated sanitized string with
+// an even number of [0-9a-f] characters, and target to be sufficiently large
+void hex2bin(const char* src, uint8_t* target)
+{
+  while(*src && src[1])
+  {
+    *(target++) = char2int(*src)*16 + char2int(src[1]);
+    src += 2;
+  }
+}
+
+void setup(){
+  sleep(LOOP_DELAY);  // give the serial monitor a moment to connect.
+  Serial.begin(115200);
+  WiFi.mode(WIFI_MODE_STA);
+  macLocal=WiFi.macAddress();
+  macRemote=macList[macList[0]==macLocal?1:0];
+  Serial.println("Local [" + macLocal + "] -> Remote: [" + macRemote+"]");
+
+  // Init ESP-NOW
+  if (esp_now_init() != ESP_OK) {
+    Serial.println("Error initializing ESP-NOW");
+    return;
+  }
+
+  // Once ESPNow is successfully Init, we will register for Send CB to
+  // get the status of Trasnmitted packet
+  esp_now_register_send_cb(OnDataSent);
+  
+  // Register peer
+  String macRemoteNoColon=macRemote;
+  macRemoteNoColon.replace(":","");
+  char macRemoteNoColonCharArr[13];
+  macRemoteNoColon.toCharArray(macRemoteNoColonCharArr,sizeof(macRemoteNoColonCharArr));
+  
+  for (int i=0;i<12;i++){
+    Serial.print( macRemoteNoColonCharArr[i]);
+    Serial.print(".");
+  }
+  Serial.println("<--- HEX CA");
+
+  hex2bin(macRemoteNoColonCharArr,macRemoteIntArr);
+  for (int i=0;i<6;i++){
+    Serial.printf( "%d|%X - ",macRemoteIntArr[i],macRemoteIntArr[i]);
+  }
+  Serial.println("<--- DEC REM");
+  memcpy(peerInfo.peer_addr, macRemoteIntArr, 6);
+  peerInfo.channel = 0;  
+  peerInfo.encrypt = false;
+  peerInfo.ifidx = WIFI_IF_STA;
+  
+  // Add peer        
+  if (esp_now_add_peer(&peerInfo) != ESP_OK){
+    Serial.println("Failed to add peer");
+    return;
+  } 
+  
+  // Register for a callback function that will be called when data is received
+  esp_now_register_recv_cb(OnDataRecv);
+
+  pinMode(GPIO_EMERGENCY_LED, OUTPUT);
+  digitalWrite(GPIO_EMERGENCY_LED,LOW);
+  pinMode(GPIO_SYNC_LED,OUTPUT);
+  digitalWrite(GPIO_SYNC_LED,LOW);
+
+  pinMode(GPIO_EMERGENCY_BUTTON,INPUT_PULLDOWN);
+  attachInterrupt(GPIO_EMERGENCY_BUTTON, OnButtonPushed, RISING);
+
+  myData.isPing=1;
+  myData.macOfSender="";
+  isReceiverEmergencyLedOn=false;
+  myData.isEmergency=false;
+  isSenderEmergency=false;
+  lastButtonPushUptimeInSeconds=getUptimeInSeconds();
+}
+ 
+void loop(){
+  // Send message via ESP-NOW
+  sleep(LOOP_DELAY);
+  boolean isButtonPushed = (HIGH== digitalRead(GPIO_EMERGENCY_BUTTON));
+  Serial.println(isButtonPushed?"PUSHED":"RELEASED");
+
+  // only one device has a button, the origin will tell the recipient to revert back the status.
+  if (isButtonPushed) {
+    myData.macOfSender=macLocal;
+  }
+
+  if (myData.macOfSender!=macLocal) {
+    myData.isEmergency=isReceiverEmergencyLedOn;
+  } else {
+    myData.isEmergency=isSenderEmergency;
+  }
+
+  esp_err_t result = esp_now_send(macRemoteIntArr,(uint8_t *) &myData, sizeof(myData));
+  
+  Serial.println(myData.isEmergency?"EMERGENGY ON":"EMERGENCY OFF");
+  Serial.println((isSenderEmergency==1)?"SEN EMERG ON":"SEN EMERG OFF");
+  
+
+  if ((getUptimeInSeconds()-lastPingUptimeInSeconds) < (LOOP_DELAY*PING_TIMEOUT_NUM_LOOPS)) {
+    digitalWrite(GPIO_SYNC_LED,HIGH);
+  } else {
+    digitalWrite(GPIO_SYNC_LED,LOW);
+  }
+
+  switch (result) {
+    case  ESP_OK:
+      Serial.println("[" +macLocal+ "] Sent with success");
+      break;
+    case ESP_ERR_ESPNOW_NOT_FOUND:
+      Serial.println("[" +macLocal+ "] Peer not Avavilable");
+      break;
+    default:
+      Serial.printf("[%s] Error sending the data [%X]\n",macLocal,result);
+  }
+  
+}

test/README

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+
+This directory is intended for PlatformIO Test Runner and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/en/latest/advanced/unit-testing/index.html